Stephen Stoute

Planar Annular Ring Antennas With Multilayer Self-Biased NiCo-Ferrite Films Loading

With their high relative permeability, magneto-dielectric materials show great potential in antenna miniaturization. This paper presents an annular ring antenna with self-biased magnetic films loading in the gigahertz frequency range. The annular ring antenna was realized by cascading a microstrip ring and a tuning stub. Self-biased NiCo-ferrite films were adopted to load an annular ring antenna on a commercially available substrate that operates at 1.7 GHz. Novel antenna designs with self-biased NiCo-ferrite films on one side and both sides of the substrate were investigated. Antennas with self-biased magnetic films loading working at 1.7 GHz showed a down shift of 2-71 MHz of the central resonant frequency. An antenna gain enhancement of up to 0.8 dB was observed over the non-magnetic antenna.

Tunable Miniaturized Patch Antennas With Self-Biased Multilayer Magnetic Films

Magneto-dielectric substrates with thin magnetic films show great potential in realizing electrically small tunable antennas with enhanced bandwidth, improved directivity, and high efficiency. This communication introduces self-biased NiCo-ferrite magnetic films as a practical mean to tune a patch antenna by loading single layer and multilayer self-biased ferrite films. The central resonant frequency of the unloaded patch antenna is measured at 2.1 GHz with a bandwidth of 18 MHz. However, with ferrite loading of the alumina substrate, this frequency is shown to be tunable within a range of 12 MHz-40 MHz, and the antenna efficiency is increased from 41% of the non-magnetic antenna to 56%, 65%, and 74% for the three magnetic antennas. Theomnidirectional radiation pattern is significantly enhanced with the -5 dBic gain beamwidth increased from 140deg to 155deg, 156deg and 160deg, respectively for the three ferrite loaded antennas. In addition, the gains of the three magnetic antennas are enhanced by 0.32, 0.77, and 1.1 dB, respectively, over the unloaded antenna.

Strong magnetoelectric coupling in ferrite/ferroelectric multiferroic heterostructures derived by low temperature spin-spray deposition

Strong magnetoelectric (ME) interaction was demonstrated at both dc and microwave frequencies in a novel Zn0.1Fe2.9O4/PMN‐PT (lead magnesium niobate‐lead titanate) multiferroic heterostructure, which was prepared by spin-spray depositing a Zn0.1Fe2.9O4 film on a single-crystal PMN‐PT substrate at a low temperature of 90 ◦ C. A large electric-field induced ferromagnetic resonance field shift up to 140Oe was observed, corresponding to an ME coefficient of 23OecmkV −1 . In addition, a large electrostatic field tuning of the magnetic hysteresis loops was observed with a large squareness ratio change of 18%. The spin-spray deposited ferrite/piezoelectric multiferroic heterostructures exhibiting strong ME interactions at both dc and microwave frequencies provide great opportunities for novel electrostatically tunable microwave magnetic devices synthesized at a low temperature. (Some figures in this article are in colour only in the electronic version)

Spin-spray deposited multiferroic composite Ni0.23Fe2.77O4∕Pb(Zr,Ti)O3 with strong interface adhesion

Ni0.23Fe2.77O4 (NFO)/Pb(Zr,Ti)O3 (PZT) multiferroic composites were synthesized by spin-spray deposition of NFO film onto PZT at 90°C. Strong interface adhesion between NFO and PZT was observed, which was verified by high resolution transmission electron microscopy indicating excellent wetting between the NFO and PZT, and by the strong magnetoelectric coupling in the NFO/PZT multiferroic composite showing an electric field induced remnant magnetization change of 10%. This strong interface adhesion and low-temperature spin-spray synthesis of multiferroic materials provide an alternative route for novel integrated multiferroic materials and devices.

Spin-spray deposited NiZn-Ferrite films exhibiting μr′ > 50 at GHz range

Ni0.27ZnxFe2.73-xO4 (with x = 0.03−0.1) thin films with high real permeability μr′ in the GHz range were fabricated by the spin spray process onto glass substrates in the presence of an external magnetic field of 360 Oe. These films exhibit high permeabilities that exceeded the Snoek limit for bulk NiZn-ferrite films and those previously reported for spin spray deposited ferrites. The NiZn-ferrite film with x = 0.06 is low in magnetic losses, having tanδm (μr″/μr′) ∼ 0.027 from 1 to 1.5 GHz, and a high ferromagnetic resonance (FMR) frequency of 2.7 GHz, while the x = 0.1 film exhibited a high μr′ of ∼50 and μr″ > 50 at 1 GHz. These properties are ideal for microwave applications such as antennas, inductors and electromagnetic interference (EMI) suppression in the GHz range.

Miniaturized Antennas and Planar Bandpass Filters With Self-Biased NiCo-Ferrite Films

Miniaturized microwave devices are realized by using magnetodielectric substrate comprising thin magnetic films that exhibit both high permittivity and high permeability at gigahertz frequency. We have fabricated and tested miniature circular patch antennas and hairpin bandpass filters with the alumina and Rogers substrate loaded with self-biased NiCo-ferrite films that exhibit excellent uniformity and low loss at frequencies exceeding 1.5 GHz. The measured results of magnetic hairpin bandpass filters have improved the central resonant frequency shift from 1.55 to 1.44 GHz, and a large resonant frequency tunability of about 23%-34% of the - 3-dB bandwidth was achieved. For the circular patch antenna, we observed an improvement of 0.8 dB in gain and a large resonance frequency tunability of 100%-320% of the antenna -10-dB bandwidth.

Optimum design of magnetic inductive energy harvester and its AC-DC converter

The design of a new-type of inductive magnetic energy harvesting system with high permeability magnetic material combined with a dual polarity boost converter is presented. By using the strong magnetostatic interaction between the coils and permanent magnets, the output power and power density of the energy harvester is enhanced compared to conventional air cored inductive harvesters. In the proposed dual polarity boost converter, the coil leakage inductor of the harvester is utilized to form the input inductor of the boost converter to minimize the converter size. Therefore, the magnetic energy harvester and the power converter share the same magnetic core. Optimum system design becomes a balance of core size, required leakage inductance and required magnetizing inductance in order to extract maximum energy.